Classic Big Dob: 12.5” f/5 Obsession Dobsonian

The author’s 12.5″ Obsession Dobsonian telescope without the usual black shroud that covers the truss pole area. Credit: Ed Ting

Reflector telescopes on Dobsonian mounts (simple up-down-left-right bases) are popular with deep sky observers looking to get the most bang for their buck. However, once these telescopes reach 12 inches in aperture or so, traditional solid-tubed telescopes become unwieldy and heavy. Manufacturers like Obsession (and others) completely rethought the design of the traditional large-aperture reflector, and a new niche of product was born: the premium open-truss Dobsonian telescope.

The 12.5-inch f/5 is the smallest telescope in Obsession’s lineup, which goes all the way up to their massive 25-inch model (this 12.5-inch is sometimes referred to as the “Baby Obsession.”) At the bottom there is a lower rectangular mirror box/rocker box that houses the primary mirror. At the top, there is a circular upper truss assembly containing the secondary mirror and eyepiece, and there are truss poles in between. Most people can assemble the telescope in about six minutes. One benefit of this arrangement is that, once disassembled, the components take up very little space; in the case of the 12.5-inch, everything can be tucked away in the back of a closet.

The 12.5″ Obsession Dobsonian collapses into a small package for travel. Credit: Ed Ting

Other than cosmetics, what’s different about a truss-style reflector? A lot. It has a high quality mirror, usually handmade by a master optician. The motions on both axes are much smoother than those on a commercial-grade telescope. On the azimuth (left-right) axis there are large Teflon pads contacting flooring laminate – yes, the floor in your kitchen turns out to be an excellent material for ensuring smooth motions on your telescope. 

On the altitude (up-down) axis, the side bearings are massive. The larger the diameter of these side bearings, the smoother the motions. Look at the outboard metal semi-circular rings in the photos above. They are so large the top half is even cut off since you will never use them. Compare these side-bearing sizes to the smaller ones in less expensive commercial units. The result is these telescopes seem to glide under the hand. One impression that people have is that these scopes seem to “disappear” underneath you as you observe.

Obsession is a premium brand, and it carries a premium price. The base unit sells for $4495, plus any upgrades or accessories you wish to add, and delivery can run from several months to close to a year. They are made to order in the US. The name “Obsession” is apt; this brand, like other premium Dobsonian manufacturers, has a passionately loyal following. It is not unusual to see people who own two or even three of them. If you love to “go deep” into the dim, far reaches of outer space and have the means to afford one, by all means check these out.

Note: As of this writing, Obsession is transitioning from these “Classic” series of their telescopes to a newer “UC” (Ultra Compact) design that uses metal instead of wood for its structure. Check availability before ordering. A 15-inch UC Obsession is expected to arrive in the next few months here. Watch this space for a review!

For more on the 12.5” Obsession, including a demonstration on how to assemble it, watch Ed’s YouTube video:


MSRP:  $4495



About Ed Ting

Ed Ting is a well-known amateur astronomer. His work has appeared in Sky & Telescope, Night Sky, Skywatch, Amateur Astronomy, Discover, and Popular Mechanics magazines. His web site,, is a widely-read telescope review web site. He is a National Science Foundation Ambassador to Chile and a NASA Solar System Ambassador.

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